In reading my neuroscience in preparation for my class today, I think I can explain physiologically why babies move around 4-5 month. We are studying neurogenesis (development of the nervous system), and there are several major events that happen. At 22-24
days gestation, the beginnings of the nervous system (the neural tube) forms, so even before many people know they are pregnant, their baby has the beginnings of a brain/spinal cord! Then at 5 weeks gestation the 5 cerebral cesicles of the brain are formed. At 3-4 months gestation, your baby has just about all of the neurons it will every have in its life, and between 3-6 months, the neurons migrate to their final targets, and in that time, the baby has a functional nervous system! That is why it can respond to extrenal stimulus -- it has sensory neurons -- and why it can move -- it has motor neurons.
Although the final myelination doesn't occur until the baby is 6 months old - 3 years old and the baby doesn't have fine motor control, or fast sensory propogation, or even coordination, it has a completely functional nervous system.
Just thought I'd share. Okay, it is procrastination. This stuff is really boring!
- Laura
